1. Field of the Invention
This invention relates to an optical information recording and/or reproducing apparatus for effecting recording of information on and/or reproduction of information from an optical information recording medium, and in particular to an optical information reproducing apparatus for effecting reading of signals from a plurality of information bits by the use of a two-dimensional sensor array, and to an apparatus capable of reproducing the information of a plurality of tracks at one time.
2. Related Background Art
Various forms such as an optical disk, an optical card and an optical tape are known as the forms of a medium for recording and reproducing information by the use of light. These have their own characteristics and are properly used in conformity with desired purposes and uses, and among them, the optical card is considered to widen its use in the future because of its ease of manufacture, its good portability and its good accessibility.
There are optical cards of the type which are capable of recording and reproduction, and of the type which are capable of only reproduction. As an optical card of the type which is capable of only reproduction, there is known one in which information is formed as binary signal patterns of different reflectances on a recording medium by a technique such as photolithography. When the information is to be reproduced, the medium surface of the optical card is illuminated and the recorded pattern on the medium surface is imaged on a sensor through an optical system to thereby read the intensity distribution of the image.
FIG. 1 of the accompanying drawings is a schematic plan view showing the recording format of an optical card according to the prior art.
In FIG. 1, a recording area 22 is provided on the optical card 1 which is a recording medium, and the recording area 22 is formed with a plurality of bands 23 arranged therein. Further, the bands 23 are formed with a number of tracks 24 arranged therein, and each track 24 has an information capacity on the order of several tens to one hundred bits. The bands 23 are partitioned by reference lines 25. The arrow A indicates the direction of movement of the optical card 1 during reproduction.
FIG. 2 of the accompanying drawings schematically shows the construction of an optical card reproducing apparatus.
In FIG. 2, the optical card 1 is movable in the direction of arrow A by a rotating mechanism 26. Information recorded on the optical card 1 is read and reproduced for each track by an optical head 31. Light, from a light source 27 such as an LED is condensed on the optical card 1 by an illuminating optical system 28 and illuminates the optical card 1. An imaging optical system 29 is disposed so that the optical axis thereof is in the exact opposite relation with the optical axis of the illuminating optical system 28 relative to the medium surface of the optical card 1, and the light flux reflected on the optical card 1 is imaged on a one-dimensional sensor array 30 by the imaging optical system 29, and an electrical signal corresponding to the information recorded on the track 24 is output from the sensor array 30. When the reading of the track 24 is terminated, the optical card 1 is moved in the direction of arrow A or the optical head 31 is moved in the direction of arrangement of the bands 23 (the direction of arrow C in FIG. 1), and the reading of the information of the next track is effected in a similar manner.
FIG. 3 of the accompanying drawings schematically shows the construction of another example of the optical card reproducing apparatus according to the prior art. The apparatus shown in FIG. 3 is similar in basic construction to the apparatus of FIG. 2, but partly differs in the optical system device of the optical head 32. That is, the light from the light source 27 such as an LED vertically illuminates the medium surface of the optical card 1 via a half-mirror 33 and an optical system 34 serves both as an illuminating system and an imaging system, and the light flux reflected by the medium surface passes through the optical system 34 and is thereafter reflected by the half-mirror 33 and is imaged on the one-dimensional sensor array 30. In the other points, the construction and operation of the apparatus of FIG. 3 are similar to those of the apparatus of FIG. 2.
However, there have been several problems when the information is to be reproduced from the optical card by the use of such a prior-art reproducing apparatus.
The first problem arises when the reproducing apparatus as shown in FIG. 2 is used. It is that since the optical axes of the illuminating system 28 of the optical head and the imaging optical system 29 are inclined with respect to the medium surface of the optical card 1, the imaging position on the one-dimensional sensor array is moved by the inclination or the vertical movement of the medium surface and deviates from the light-receiving surface of the sensor and thus, information reproduction fails to be correctly accomplished in some cases.
The second problem arises when the reproducing apparatus as shown in FIG. 3 is used. If the light source 27 such as an LED is used for illumination, the light flux emitted from the light source 27 is transmitted through and is reflected by the half mirror 33, whereafter it arrives at the sensor 30 and therefore, the quantity of light decreases remarkably. Therefore, if an attempt is made to increase the reproducing speed, it is necessary to use an expensive LED of high luminance or use a sensor of high sensitivity, but there is a limit in any of these countermeasures, and cost unavoidably becomes higher as a reproducing apparatus used for the reproduction of a medium such as the optical card 1 which is used in great quantity.
Here, if a semiconductor laser is used instead of an LED, the above-noted problem can be solved even by a laser of relatively low output and accordingly low cost due to its high luminance and its good directionality. However, a new problem will arise. That is, due to the high coherency of the laser, the light reflected by the surface of the optical card 1 and the light reflected by the medium surface interfere with each other, whereby harmful interference fringes are formed on the sensor and they appear as noise in reproduced signals. In such a case, forming an anti-reflection film on the surface of the optical card results in a higher cost as the medium used in great quantity as previously described, and this is not preferable. Also, the film may peel off during transportation and this in turn leads to a problem in practical use.
As another example of the optical card according to the prior art, there is one which is capable of both recording and reproduction as previously described. Description will hereinafter be made of an information recording-reproducing apparatus according to the prior art using such an optical card.
Here, various methods of causing a light beam applied to the optical card to scan the optical card are conceivable, but a method whereby the applied position of the light beam is reciprocally moved relatively straight on the medium and the applied position of the beam is relatively moved sequentially on the medium in a direction orthogonal to the direction of the reciprocal movement is characterized in that the mechanism is simple and the effective space on the medium is large.
An example of the optical information recording-reproducing apparatus adopting such a method is shown in FIG. 4 of the accompanying drawings. FIG. 4 is a block diagram of the apparatus.
In FIG. 4, the reference numeral 41 designates an optical card on which information is to be recorded, the reference numeral 43 denotes an optical head (the portion outlined by a dotted line in FIG. 4), the reference numeral 44 designates a light beam, the reference numeral 45 denotes a supporting table for supporting the optical card 41 thereon, the reference numeral 48 designates a laser, and the reference numeral 49 denotes a collimator lens. The reference numeral 50 designates a polarizing beam splitter, and the reference numeral 70 denotes a quarter wavelength plate, and the light travelling downward as viewed in FIG. 4 is transmitted by a combination of these two members, but the light travelling upward as viewed in FIG. 4 is bent in a perpendicular direction. The reference numeral 51 designates a pick-up lens which serves to condense a parallel light on the optical card 41.
The reference numeral 52 denotes a photosensor, the reference numeral 53 designates a preamplifier, the reference numeral 54 denotes an auto focusing servo, the reference numeral 55 designates an auto tracking servo, the reference numeral 56 denotes a decoder, the reference numeral 57 designates an interface, the reference numeral 58 denotes a computer, the reference numeral 59 designates an encoder, the reference numeral 60 denotes a laser driver, and the reference numeral 61 designates a stepping motor which serves to move the optical head 43 in a direction perpendicular to the plane of the drawing sheet.
The reference numerals 62 and 63 denote pulleys over which a belt 64 is passed. The supporting table 45 for supporting and fixing the optical card 41 thereon is mounted on the belt 64. The pulley 62 is mounted on the shaft of a motor 66, and the optical card 41 is reciprocally moved in the direction of arrow A by the revolution of the motor 66.
The operation of the apparatus shown in FIG. 4 will now be described. Description will first be made of the case of reproduction. In FIG. 4, a light beam emitted from the laser 48 is collimated by the collimator lens 49, passes through the polarizing beam splitter 50 and the quarter wavelength plate 70, is condensed by the pick-up lens 51 and forms a minute spot on the optical card 41. The reflected light from the optical card 41 is modulated depending on whether there is an information pit in the portion irradiated by the minute spot, and this modulated light is again made into parallel light by the pick-up lens 51 and is caused to enter the photosensor 52 by the polarizing beam splitter 50. The photosensor 52 detects any variation in the quantity of the modulated light, and converts the variation into an electrical signal and supplies it to the preamplifier 53. A signal is supplied from the preamplifier 53 to the auto focusing servo 54, and the pick-up lens 51 is moved in the direction of arrow B by the signal from the auto focusing servo 54 with the aid of an actuator, not shown, whereby the distance between the pick-up lens 51 and the optical card 41 is controlled so that the light beam 44 is focused on the optical card 41.
A signal is also supplied from the preamplifier 53 to the auto tracking servo 55, and the signal from the auto tracking servo 55 moves the pick-up lens 51 in a direction perpendicular to the plane of the drawing sheet with the aid of the actuator, not shown, to thereby control the light beam 44 so as to be focused at a predetermined position. Several specific methods have been proposed regarding the auto focusing servo 54 and the auto tracking servo 55, and for example, there is proposed an example in which the light beam 44 is divided into a plurality of beams by a grating or the like to preform a track for auto focusing or auto tracking (hereinafter referred to as the guide track) on the optical card 41 and information is reproduced by at least one of the plurality of light beams and signals for auto focusing and auto tracking are taken out by the other beams.
Further, the signal from the preamplifier 53 is sent to the decoder 56, in which it is subjected to electrically necessary processing, and is thereafter supplied to the interface 57. From the interface 57, an information signal is sent to the computer 58. Also, from the interface 57, a signal is sent to the encoder 59, and is modulated as required, whereafter it controls the oscillation of the laser 48 via the laser driver 60.
Further, from the interface 57, a signal is sent to the stepping motor 61 and the motor servo 67, whereby control of the position of the optical head 43 in a direction perpendicular to the plane of the drawing sheet and control of the revolution of the motor 66 are effected.
Description will now be made of the case of recording. Again in the case of recording, the operation is substantially similar to the operation in the case of reproduction, but in the case of recording, a light stronger than in the case of reproduction is emitted from the laser 48. As in the case of reproduction, the light beam is imaged on the optical card 41 and information is recorded on the optical card 41 in accordance with the modulation of the laser beam. Again in the case of recording, it is usually necessary to effect auto focusing or auto tracking, and various methods therefor have been proposed. For example, the light beam is divided into at least one strong beam (for writing) and at least one weak beam (for focusing or auto tracking) by means such as a grating, and writing can be accomplished by the strong beam while the guide track preformed on the optical card 41 is being tracked by the weak beam.
In the recording-reproducing apparatus described above, information pits are recorded or reproduced one by one by the rectilinear reciprocal movement of the optical card. However, the apparatus having such a function suffers from the disadvantage that a long time is required particularly when a great deal of information is to be reproduced. As a means for solving this, there is conceived a method of increasing the speed of the reciprocal movement of the card, but this method in turn has the difficulty that mechanical vibration is increased to adversely affect the reproduced signal or increase the load of the card feeding mechanism or the motor.
If reproduction alone is to be effected, the speed of the reciprocal movement of the card can be decreased by using a method of reading a plurality of information tracks at one time by the use of a line sensor such as a CCD, but to add such a line sensor to an apparatus for both recording and reproduction, presents the necessity of carrying a discrete head exclusively for reading on the apparatus, which in turn avoidably leads to the bulkiness and complication of the apparatus, and sometimes to the necessity of additionally providing auto focusing and auto tracking mechanisms to the head exclusively for reading.
Also, to read a plurality of information tracks at one time, it is necessary to illuminate these tracks at one time, but if an incoherent light source such as an LED is used for this purpose, it will be difficult to illuminate the necessary area with a high intensity of illumination, and it will also become difficult to increase the reproduction rate because the utilization rate of the light is reduced by the light passing through a beam splitter in the optical head.
If a light source being in a rectilinearly polarized state and having high luminance, such as a semiconductor laser, is used, an isolated optical system using a combination of a polarizing beam splitter and a wavelength plate can be used. Therefore, the utilization rate of the light is improved, while the reflected light from the surface of the protective layer of the optical card is superposed on and interferes with the reflected light from the medium surface, and as in the aforedescribed reproducing apparatus, this leads to the new problem that noise harmful to the reproduction of signals is produced.